Retroreflection sheet

ABSTRACT

An original sheet of a retroreflective sheet includes plural glass beads with a metal reflective layer provided on lower hemisphere surfaces thereof, a resin support sheet for supporting the glass beads, and a transparent cover film disposed on a surface side of the resin support sheet, wherein the resin support sheet and the cover film are connected to each other by heat press emboss forming from a rear face of the resin support sheet so as to form the original sheet of the retroreflective sheet, and a retroreflective sheet laminate includes a pressure-sensitive adhesive layer and a resin release film for covering the pressure-sensitive adhesive layer on a rear side of the original sheet of the retroreflective sheet. An embossed groove by heat press emboss forming was filled with a part of the pressure-sensitive adhesive layer, a residual rate of the pressure-sensitive adhesive layer ranges between 10% and 50% inclusive, and a fall time of the pressure-sensitive adhesive layer ranges between 10 hours and 150 hours inclusive.

TECHNICAL FIELD

The present invention relates to a retroreflective sheet used fortraffic signs, guide signs, sign boards for safety guidance, or othersafety signs.

BACKGROUND ART

Retroreflective sheets are widely used mainly for traffic safetypurposes such as traffic signs, guide signs, warning signs, restrictionsigns. The retroreflective sheet includes plural retroreflectiveelements, a resin support sheet, a transparent cover film disposed on asurface side of the resin support sheet and a pressure-sensitiveadhesive layer on a rear face side of the resin support sheet. Theretroreflective element is supported by at least one of the resinsupport sheet and the cover film, and the resin support sheet and thecover film are connected to each other by heat press emboss forming fromthe rear face of the resin support sheet so as to form a connectionpart. A groove of the connection part is formed on the rear face side ofthe resin support sheet. A release film is further laminated to theretroreflective sheet. For the release film, a release material, such asa polyester film, a polyethylene laminated paper, polypropylene andpolyethylene, coated with a release agent such as a silicon compound anda fluorine compound, may be used. For a pressure-sensitive adhesive forforming the pressure-sensitive adhesive layer, a solvent-typepressure-sensitive adhesive, an emulsion-type pressure-sensitiveadhesive, and a pressure-sensitive adhesives that can be cured byelectron beams or ultraviolet rays, or the like may be used, forexample. Such a retroreflective sheet is adhered to a substrate such asa metal substrate like aluminum, a steel plate, a coated steel plate anda stainless steel plate; a plastic substrate like a fiber reinforcedplastic (FRP) and a rigid vinyl chloride; and a composite substrateincluding aluminum plates sandwiching polyethylene or the like, by usingan adhesion device or an adhesion machine such as a squeegee, a handroll and a mangle roll, so as to be used as a display board, a signboardor the like (see JP3278299 and JP2000-329918A, the contents of which areincorporated by reference).

However, when adhering the retroreflective sheet to the substrate,unless air trapped between the substrate and the retroreflective sheetis expelled, the air is enclosed between the substrate and theretroreflective sheet. In this case, when a temperature of the substrateincreases due to sunlight or the like, the enclosed air expands, andaccordingly a trouble such as blisters, bubbles, wrinkles andexfoliations may occur to the retroreflective sheet. In order to preventthis, when adhering the retroreflective sheet to the substrate, it isnecessary to apply some pressure so as to expel the air trapped betweenthe substrate and the retroreflective sheet. In addition, in the casewhere the retroreflective sheet in a distorted state is adhered to thesubstrate, problems such as blisters, bubbles, wrinkles, exfoliations orthe like occur over the course of time due to a residual stress insidethe retroreflective sheet.

DISCLOSURE OF THE INVENTION

However, any effective measures have not been taken against thisproblem. According to the above-cited JP3278299, for example, aretroreflective sheet for a gas-generating adherend is proposed forpreventing the blisters of the retroreflective sheet. Thisretroreflective sheet for a gas-generating adherend includes apressure-sensitive adhesive for forming a pressure-sensitive adhesivelayer, which is made of a resin obtained by a cross-linking reaction tocross-linking resins having a weight-average molecular weight of 500,000or more, the holding power is 10 mm/1000 min or less at 100° C., and awetting with respect to a polycarbonate resin plate is 50% or more after30 minutes from adhesion. Actually, however, even by using thepressure-sensitive adhesive satisfying this condition to prevent theblisters and the like of the retroreflective sheet, the above-mentionedproblem was not solved sufficiently.

In addition, JP2000-329918A proposes use of the groove of the resinsupport sheet, which is formed during heat press emboss forming, fordischarging the air. However, when the retroreflective sheet is usedoutdoors as a sign board, contaminants such as water, dirt, dusts mayintrude in the groove, degrading a sticking property, and troubles suchas exfoliations and peeling of the sheet may occur. In order to preventthese troubles, it is necessary to expel the air in the groove at thetime of adhesion of the retroreflective sheet, and to fill the groovewith a pressure-sensitive adhesive layer. For this purpose, it isnecessary to lower a cohesive power of the pressure-sensitive adhesiveso that the pressure-sensitive adhesive layer may enter the grooveeasily. Whereas, in the case where the retroreflective sheet isdistorted at the time of its adhesion, a residual stress in theretroreflective sheet may cause blisters, bubbles, wrinkles,exfoliations and the like to the sheet over the course of time. However,because the cohesive power of the pressure-sensitive adhesive islowered, the retroreflective sheet cannot resist this stress, therebycausing cohesive failure of the pressure-sensitive adhesive.Consequently, the retroreflective sheet cannot stop its movement causedby the residual stress, so that blisters, bubbles, wrinkles,exfoliations or the like occur in the retroreflective sheet. In thelight of these conditions, development of a new retroreflective sheetwhich is prevented from the occurrence of blisters, bubbles, wrinkles,exfoliations or the like has been desired in the market.

In order to solve the above-stated conventional problem, the presentinvention has an object to provide a retroreflective sheet that can beprevented from an appearance abnormality such as blisters, bubbles,wrinkles, exfoliations, which may occur over the course of time afterthe adhesion to a substrate.

In order to attain the above-mentioned object, the retroreflective sheetof the present invention includes plural retroreflective elements, aresin support sheet, a transparent cover film disposed on a surface sideof the resin support sheet, and a pressure-sensitive adhesive layerformed on a rear face side of the resin support sheet, wherein theretroreflective element is held in at least one of the resin supportsheet and the cover film, the resin support sheet and the cover film areconnected to each other by heat press emboss forming from the rear faceside of the resin support sheet so as to form a connection part, agroove of the connection part is formed on the rear face side of theresin support sheet, the groove is filled with a part of thepressure-sensitive adhesive layer, a residual rate of thepressure-sensitive adhesive layer ranges between 10% and 50% inclusive,and a fall time of the pressure-sensitive adhesive layer ranges between10 hours and 150 hours inclusive: where residual rate (%)=(a residualdisplacement÷an initial displacement)×100, the initial displacementrepresents a displacement (mm) between a flat plate and theretroreflective sheet measured by a Yamamoto's cohesion tester, whichoccurs after 5 minutes from steps of: pressing the retroreflective sheetwith a size of 10 mm×5 mm onto the mirror-surfaced flat plate of aSUS304 steel plate specified by JISG 4305 with a width of 5 mm, using apressing device specified by JIS Z 0237; adding loads of 17 grespectively to both ends of the retroreflective sheet via stringsimmediately after the pressing; and further applying a measurement loadof 200 g to one of the loads, the residual displacement represents adisplacement occurring between the flat plate and the retroreflectivesheet after 10 minutes from removal of the load of 200 g, and the falltime represents a fall time of the retroreflective sheet with a load of9.8 N imposed in a holding power test at 40° C. in accordance with aJISZ0237 holding power test.

A method for manufacturing a laminate of a heat-resistant releasematerial and the retroreflective sheet of the present invention includessteps of: preparing an original sheet of a retroreflective sheetincluding plural retroreflective elements, a resin support sheet, and atransparent cover film disposed on a surface side of the resin supportsheet, in which the retroreflective element is held in at least one ofthe resin support sheet and the cover film, the resin support sheet andthe cover film are connected to each other by heat press emboss formingfrom a rear face of the resin support sheet so as to form a connectionpart, and a groove of the connection part is formed on the rear faceside of the resin support sheet; forming a pressure-sensitive adhesivelayer on the heat-resistant release material; and disposing theheat-resistant release material with the pressure-sensitive adhesivelayer formed thereon on the rear face side of the original sheet of theretroreflective sheet, adhering them to each other by inter-roll linepressure ranging between 100 N/cm and 800 N/cm inclusive at a rollsurface temperature ranging between 50° C. and 90° C. inclusive from aheat-resistant release material side, so that the groove of the resinsupport sheet is filled with a part of the pressure-sensitive adhesivelayer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view showing a process of forming areflective layer on glass beads, according to an example of themanufacturing method of the present invention.

FIG. 2 is a cross-sectional view showing a process of forming a resinsupport sheet, according to an example of the manufacturing method ofthe present invention.

FIG. 3 is a cross-sectional view showing a process of transferring glassbeads, according to an example of the manufacturing method of thepresent invention.

FIG. 4 is a cross-sectional view showing a process of embedding glassbeads in a resin support sheet, according to an example of themanufacturing method of the present invention.

FIG. 5 is a cross-sectional view showing a process of exposingantireflection surfaces of glass beads, according to an example of themanufacturing method of the present invention.

FIG. 6 is a cross-sectional view showing a process of heat press embossforming from a rear face side of a resin support sheet, according to anexample of the manufacturing method of the present invention.

FIG. 7 is a cross-sectional view showing a process of heat press embossforming, according to an example of the manufacturing method of thepresent invention.

FIG. 8 is a cross-sectional view showing a process of covering a heatpress emboss formed side with a heat-resistant release material having apressure-sensitive adhesive layer formed thereon, according to anexample of the manufacturing method of the present invention.

FIG. 9 is a cross-sectional view showing a process of adhering a resinrelease film instead of a heat-resistant release material, according toan example of the manufacturing method of the present invention.

FIG. 10 is a cross-sectional view showing a capsule cube corner typeretroreflective sheet after heat press emboss forming, according to anexample of the manufacturing method of the present invention.

FIG. 11 is a view describing a method for an appearance measurementadapted in the examples of the present invention.

FIG. 12 is a illustrative view describing a measurement method using aYamamoto's cohesion tester which is employed in the examples of thepresent invention.

FIG. 13 is a schematic perspective reference view of a Yamamoto'scohesion tester employed in the examples of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The retroreflective sheet of the present invention can be prevented froman appearance abnormality which occurs over the course of time afteradhesion to a substrate.

The inventors of the present invention found that, by reducing the airremaining between the retroreflective sheet and the substrate when theretroreflective sheet is adhered, the appearance abnormality of theretroreflective sheet, which occurs over the course of time after theadhesion to the substrate, can be prevented. They also found that, evenwhen the retroreflective sheet is adhered in a distorted state, theappearance abnormality of the retroreflective sheet can be prevented byrelaxing a residual stress in the retroreflective sheet by apressure-sensitive adhesive layer that is disposed on a rear face sideof the resin support sheet.

The inventors also found that the air remaining at the time of adhesionof the retroreflective sheet can be reduced, and the residual stress inthe retroreflective sheet after the adhesion can be relaxed by: (1)filling a groove formed during heat press emboss forming, with apressure-sensitive adhesive layer in advance; (2) specifying a residualrate of the pressure-sensitive adhesive layer in a specific range, whichis obtained by a residual displacement and an initial displacement usinga Yamamoto's cohesion tester; and (3) specifying a fall time of thepressure-sensitive adhesive layer in a specific range, thereby leadingto the present invention.

The retroreflective sheet of the present invention will be describedbelow further in detail.

In the retroreflective sheet of the present invention, a thickness ofthe pressure-sensitive adhesive layer at a part where the groove is notformed on the rear face side of the resin support sheet preferablyranges between 20 μm and 110 μm inclusive, more preferably ranges from30 μm to 100 μm, particularly preferably ranges from 40 μm to 90 μm.When the thickness is 20 μm or more, the groove of the resin supportsheet may be filled with a part of the pressure-sensitive adhesivelayer, the thickness is sufficient to uniformalize the thickness of thewhole pressure-sensitive adhesive layer, and a sufficient adhesiveproperty can be obtained. When the thickness is 110 μm or less, run ofthe pressure-sensitive adhesive can be prevented, in particular, a runof the pressure-sensitive adhesive from edges, and adhesion of thepressure-sensitive adhesive to slitter blade are prevented when cuttingthe sheet into a standard size by a slitter, and furthermore, cohesivefailure of the pressure-sensitive adhesive hardly occurs.

In the retroreflective sheet of the present invention, a filling factorof the pressure-sensitive adhesive layer in the groove is preferably 50%or more.The filling factor (%)=[(A−B)÷A]×100The letter A denotes an area of the groove per unit area of theretroreflective sheet, and the letter B denotes an area of an openinggap formed on an interface between the groove and the pressure-sensitiveadhesive layer per unit area of the retroreflective sheet.

Note here that the above-mentioned “fill” means a state where the grooveis filled with a part of the pressure-sensitive adhesive layer. Thefilling factor is preferably 60% or larger, and more preferably 70% orlarger. When the filling factor is 50% or larger, air between theretroreflective sheet and the substrate can be exhaled sufficiently atthe time of the adhesion of the retroreflective sheet to the substrate.

In the retroreflective sheet of the present invention, the residual rateranges between 10% and 50% inclusive, preferably ranges between 15% and45% inclusive, more preferably ranges between 20% and 40% inclusive. Theresidual rate represents a stress relaxation property of thepressure-sensitive adhesive layer. When the residual rate is in therange between 10% and 50% inclusive, an residual internal stress in theretroreflective sheet is relaxed by the pressure-sensitive adhesivelayer at the time of the adhesion of the retroreflective sheet, thuspreventing an appearance abnormality that occurs over the course oftime, such as wrinkles, blisters, bubbles and exfoliations.

In the retroreflective sheet of the present invention, the fall timeranges between 10 hours and 150 hours inclusive, preferably rangesbetween 20 hours and 140 hours inclusive, more preferably ranges between40 hours and 130 hours inclusive. The fall time represents a cohesivepower of the pressure-sensitive adhesive layer. When the fall time is 10hours or longer, the cohesive power of the pressure-sensitive adhesivelayer is strong enough to resist a shrinkage stress of theretroreflective sheet, so that the retroreflective sheet is not shrunk.Moreover, when the fall time is 150 hours or shorter, since the cohesivepower of the pressure-sensitive adhesive is not too high, a residualinternal stress in the retroreflective sheet is relaxed by thepressure-sensitive adhesive layer by the time when the retroreflectivesheet is actually used, so that the occurrence of wrinkles, blisters,bubbles, exfoliations and the like in a main body of the retroreflectivesheet can be prevented after the application of the retroreflectivesheet.

In the retroreflective sheet of the present invention, the residual rateand the fall time of the pressure-sensitive adhesive layer arepreferably the same as a residual rate and a fall time measured when theretroreflective sheet is actually used, or a residual rate and a falltime measured after steps of forming the pressure-sensitive adhesivelayer on the rear face side of the resin support sheet and performingaging treatment at a temperature of 23±2° C. and a relative humidity of65±5% for 7 days.

Moreover, in the retroreflective sheet of the present invention, theresidual rate and the fall time of the pressure-sensitive adhesive layerare preferably the same as a residual rate and a fall time measuredafter steps of forming the pressure-sensitive adhesive layer on the rearface side of the resin support sheet, performing the above-stated agingtreatment, and further performing aging treatment at a temperature of50° C. and a relative humidity of 65±5% for 10 days.

The pressure-sensitive adhesive layer of the present invention ispreferably formed of a resin such as an acrylic resin and a rubber-basedresin. For the acrylic resin, in particular, a polymer-based acrylicresin containing at least one of an acrylic ester copolymer and anacrylic prepolymer as a main component, or a modified acrylic resinobtained by adding, to the acrylic resin, a tackifier and a monomer forproviding a cohesive power.

Examples of the rubber-based resin include a natural rubber and asynthetic rubber such as an isoprene rubber, a styrene-butadiene blockcopolymer, a styrene-isoprene-styrene block copolymer, a butyl rubber, astyrene-ethylene-butylene-styrene copolymer, a polyisobutylene, apolyvinyl isobutyl ether, a chloroprene rubber, and a nitrile rubber.

To these rubber-based resins, for example, a natural resin such as arosin, a modified rosin, derivatives of a rosin and a modified rosin, aterpenephenol resin, a polyterpene resin, a modified terpene, analiphatic hydrocarbon resin, a cyclopentadiene resin, an aromaticpetroleum resin, a phenol resin, an alkylphenol-acetylene resin, acoumarone-indene resin, a tackifier such as avinyltoluene-α-methylstyrene copolymer, various plasticizers, anantioxidant, a stabilizer, a softener such as oil, a filler, astabilizer, a pigment, a colorant, and the like may be added asnecessary. They also may be used in combination of two or more asnecessary.

Examples of the acrylic resin include a polymer or a copolymer of anacrylic vinyl monomer having an alkyl group, a hydroxyl group, an epoxygroup, an alkoxy group, a phenoxy group, an oxyethylene group, an aminogroup, an amide group, a carboxyl group, a halogen atom, a phosphategroup, a sulfonic group, an urethane group, a phenyl group, a benzylgroup, a tetrahydrofurfuryl group or the like, and a copolymer ofacrylic vinyl monomers and other copolymerizable monomers.

Examples of the acrylic vinyl monomer having an alkyl group includemethyl(meth)acrylate, ethyl(meth)acrylate, isopropyl(meth)acrylate,lauryl(meth)acrylate, stearyl(meth)acrylate, butyl(meth)acrylate,hexyl(meth)acrylate, cyclohexyl(meth)acrylate,2-ethylhexyl(meth)acrylate, isoamyl(meth)acrylate,isooctyl(meth)acrylate, n-octyl(meth)acrylate, dodecyl(meth)acrylate,isobutyl(meth)acrylate and the like.

Examples of the acrylic vinyl monomer having a hydroxyl group include2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,2-hydroxybutyl(meth)acrylate, 3-chloro-2-hydroxypropyl(meth)acrylate andthe like.

Examples of the acrylic vinyl monomer having an epoxy group includeglycidyl(meth)acrylate, methylglycidyl(meth)acrylate and the like.

Examples of the acrylic vinyl monomer having an alkoxy group includemethoxyethyl(meth)acrylate, ethoxyethyl(meth)acrylate,butoxyethyl(meth)acrylate and the like.

Examples of the acrylic vinyl monomer having a phenoxy group includephenoxyethyl(meth)acrylate and the like.

Examples of the acrylic vinyl monomer having an oxyethylene groupinclude diethyleneglycol(meth)acrylate, methoxydiethyleneglycol(meth)acrylate, methoxypolyethyleneglycol(meth)acrylate,phenoxydiethyleneglycol(meth) acrylate,phenoxypolyethyleneglycol(meth)acrylate and the like.

Examples of the acrylic vinyl monomer having an amino group includedimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate,N-tert-butylaminoethyl(meth)acrylate,methacryloyloxyethyltrimethylammoniumchloride(meth)acrylate and thelike.

Examples of the acrylic vinyl monomer having an amide group include(meth)acrylamide, N-methylol(meth)acrylamide,N-methoxymethyl(meth)acrylamide, N,N′-methylenebis(meth)acrylamide andthe like.

Examples of the acrylic vinyl monomer having a carboxyl group includeacrylic acid, methacrylic acid, 2-methacryloyloxy succinic acid,2-methacryloyloxyethyl maleic acid, 2-methacryloyloxyethylphthalic acid,2-methacryloyloxyethylhexahydrophthalic acid and the like.

Examples of the acrylic vinyl monomer having a halogen atom includetrifluoroethyl(meth)acrylate, pentadecafluorooxyethyl(meth)acrylate,2-chloroethyl(meth)acrylate, 2,3-dibromopropyl(meth)acrylate,tribromophenyl(meth)acrylate and the like.

Examples of the acrylic vinyl monomer having a phosphate group include2-methacryloyloxyethyldiphenylphosphate(meth)acrylate,trimethacryloyloxyethylphosphate(meth)acrylate,triacryloyloxyethylphosphate(meth)acrylate and the like.

Examples of the acrylic vinyl monomer having a sulfonic group includesodium sulfopropyl(meth)acrylate, sodium 2-sulfoethyl(meth)acrylate,sodium 2-acrylamide-2-methylpropanesulphonate and the like.

Examples of the acrylic vinyl monomer having an urethane group includeurethane(meth)acrylate and the like.

Examples of the acrylic vinyl monomer having a phenyl group includephenyl(meth)acrylate, p-tert-butylphenyl(meth)acrylate,o-biphenyl(meth)acrylate and the like.

Examples of the acrylic vinyl monomer having a benzil group includebenzil(meth)acrylate and the like.

Examples of the acrylic vinyl monomer having a tetrahydrofurfuryl groupinclude tetrahydrofurfuryl(meth)acrylate and the like.

Examples of other monomers having the capability of copolymerizationinclude vinyl monomers having a silane group, styrene, chlorostyrene,α-methylstyrene, vinyltoluene, vinyl chloride, vinyl acetate, vinylpropionate, a vinyl alkylate compound (trade name: VEOVA 10,manufactured by Shell Chemicals Limited), acrylonitrile, vinyl pyridineand the like.

Examples of the vinyl monomers having silane groups includevinyltrimethoxysilane, vinyltriethoxysilane,vinyltris(β-methoxyethyl)silane, vinyltriacetylsilane,methacryloyloxypropyltrimethoxysilane and the like.

In addition, examples of the other monomers having the capability ofcopolymerization include, ethyleneglycoldi(meth)acrylate,diethyleneglycoldi(meth)acrylate, triethyleneglycoldi(meth)acrylate,dipropyleneglycoldi(meth)acrylate, 1,3-butyleneglycoldi(meth)acrylate,trimethylolpropanetri(meth)acrylate,tetramethylolmethanetetra(meth)acrylate, divinylbenzene,N,N′-methylenebisacrylamide, 1,4-buthanedioldi(meth)acrylate,1,6-hexanedioldi(meth)acrylate and the like. These monomers can be usedat an extent to which coating suitability may not be degraded.

Moreover, as various additives, for example, a natural resin such as arosin, a modified rosin, derivatives of a rosin or a modified rosin, apolyterpene resin, a modified terpene, a terpenephenol resin, analiphatic hydrocarbon resin, a cyclopentadiene resin, an aromaticpetroleum resin, a phenol resin, an alkylphenol-acetylene resin, acoumarone-indene resin, a tackifier such as avinyltoluene-α-methylstyrene copolymer, various plasticizers, anantioxidant, a stabilizer, a softner such as oil, a filler, a colorant,a pigment or the like can be added to the acrylic resin as necessary.They also may be used in combination of two or more as necessary.

The above-noted acrylic resins are manufactured by polymerization usingany one of conventionally known methods such as a bulk polymerizationmethod, a solution polymerization method, a suspension polymerizationmethod and an emulsion polymerization method.

Here, monomer concentration at the polymerization generally ranges from30 wt % to 70 wt %, and preferably ranges from 40 wt % to 60 wt %,approximately.

Furthermore, a thickening agent, a wet agent, a leveling agent, anantifoaming agent or the like may be added to the resin for forming thepressure-sensitive adhesive layer, as appropriate. When a cross-linkingacrylic copolymer having a functional group is used as the acrylicresin, it is preferable to add a hardening agent having a reactivefunctional group that reacts with the above-mentioned functional group.When an acrylic copolymer that is not cross-linking is used as theacrylic resin, a hardening agent can be added as appropriate. In thecase where a hardening agent is added, the hardening agent is preferablyselected so that the pressure-sensitive adhesive layer may have aresidual rate and a fall time within the range of the present invention,after being formed in the groove of the retroreflective sheet. Forexample, in the retroreflective sheet of the present invention, thepressure-sensitive adhesive layer is preferably formed of apressure-sensitive adhesive composition including a cross-linkingacrylic copolymer and a hardening agent.

In the case where the hardening agent is added to the cross-linkingacrylic copolymer having a functional group, a content of the hardeningagent is determined depending on kinds of a functional group and asubstituent in the acrylic resin, and combination with the hardeningagent, so that a pressure-sensitive adhesive layer is formed. Thecontent of the hardening agent and the cross-linking acrylic copolymeris preferably selected so that the content thereof may allow theresidual rate and a fall time of the pressure-sensitive adhesive layerto be in the range specified in the present invention after thepressure-sensitive adhesive layer is further subjected to agingtreatment under an atmosphere of 23±2° C. and a relative humidity of65±5% for 7 days.

In the retroreflective sheet of the present invention, thepressure-sensitive adhesive layer may be formed by applying a solutionof the resin on a heat-resistant release material and subsequentlydrying by heat at 70° C. for 1 minute and at 100° C. for 2 minutes.

Examples of the hardening agent include an epoxy hardening agent, anisocyanate hardening agent, an aminoplast hardening agent, an ionichardening agent and the like. The epoxy hardening agent may besorbitolpolyglycidylether, polyglycerolpolyglycidylether,pentaerythritolpolyglycidylether, diglycerolpolyglycidylether,triglycidyl-tris(2-hydroxyethylyisocyanurate, glycerolpolyglycidylether,trimethylolpropanepolyglycidylether, resorcindiglycidylether,neopentylglycoldiglycidylether, 1,6-hexandioldiglycidylether,bisphenol-S-diglycidylether, ethyleneglycoldiglycidylether,polyethyleneglycoldiglycidylether, propyleneglycoldiglycidylether,diglycidylester adipate, diglycidylether o-phthalate and the like. Theisocyanate hardening agent may be toluylenediisocyanate, a2,4-toluylenediisocyanate dimer, naphthylene-1,5-diisocyanate,o-toluylenediisocyanate, diphenylmethanediisocyanate,triphenylmethanetriisocyanate, tris(p-isocyanatephenyl)thiophosphate,polymethylenepolyphenylisocyanate, hexamethylenediisocyanate,trimethylhexamethylenediisocyanate, isophoronediisocyanate,xylylenediisocyanate, a polyisocyanate prepolymer and the like. Theaminoplast hardening agent may be a condensate or the like, which isobtained by reacting various amono-group-containing compounds such asmelamine, urea, acetoguanamine, benzoguanamine, steroguanamine andspiroguanamine, with various aldehyde compounds such as formaldehyde,paraformaldehyde, acetaldehyde and glyoxal, by an usual method. Theionic hardening agent may be zinc acetate, magnesium acetate, or calciumacetate, which includes Mg²⁺, Ca²⁺, Zn²⁺, Al³⁺ or the like.

The residual rate and the fall time of the pressure-sensitive adhesivelayer of the retroreflective sheet of the present invention can beadjusted by forming the pressure-sensitive adhesive layer bydetermining, for example, appropriate kinds and contents of a resin anda hardening agent as materials of the pressure-sensitive adhesive layer.

The retroreflective sheet laminate of the present invention includes theretroreflective sheet of the present invention and a resin release film,in which the resin release film is laminated on the pressure-sensitiveadhesive layer.

In the retroreflective sheet laminate of the present invention, theresin release film is preferably a flexible resin film with Young'smodulus ranging between 50 MPa and 2000 MPa inclusive. More preferably,the Young's modulus thereof ranges between 100 MPa and 1500 MPainclusive, and further preferably, ranges between 150 MPa and 1000 MPainclusive.

In the retroreflective sheet laminate of the present invention, theflexible resin film is preferably an unstretched polypropylene (PP) filmor a low-density polyethylene (LDPE) film.

In the retroreflective sheet laminate of the present invention, athickness of the unstretched polypropylene film preferably rangesbetween 20 μm and 150 μm inclusive. More preferably, the thicknessranges between 30 μm and 130 μm inclusive, and further preferably,ranges between 40 μm and 100 μm inclusive.

In the retroreflective sheet laminate of the present invention, athickness of the low-density polyethylene film preferably ranges between20 μm and 200 μm inclusive. More preferably, the thickness rangesbetween 40 μm and 150 μm inclusive, and further more preferably, rangesbetween 60 μm and 100 μm inclusive.

The method for manufacturing a laminate of a heat-resistant releasematerial and the retroreflective sheet of the present inventionincludes, as mentioned above, steps of: preparing an original sheet of aretroreflective sheet including plural retroreflective elements, a resinsupport sheet, and a transparent cover film disposed on a surface sideof the resin support sheet, in which the retroreflective element is heldin at least one of the resin support sheet and the cover film, the resinsupport sheet and the cover film are connected to each other by heatpress emboss forming from a rear face of the resin support sheet so asto form a connection part, and a groove of the connection part is formedon the rear face side of the resin support sheet; forming apressure-sensitive adhesive layer on the heat-resistant releasematerial; and filling the groove of the resin support sheet with a partof the pressure-sensitive adhesive layer by disposing the heat-resistantrelease material with the pressure-sensitive adhesive layer formedthereon on the rear face side of the original sheet of theretroreflective sheet, and adhering them to each other by inter-rollline pressure ranging between 100 N/cm and 800 N/cm inclusive at a rollsurface temperature ranging between 50° C. and 90° C. inclusive from aheat-resistant release material side.

It is preferable that the above-mentioned manufacturing method furtherincludes a step of aging the pressure-sensitive adhesive layer at 23±2°C. and a relative humidity of 65±5% for 7 days.

In the manufacturing method, the heat-resistant release material ispreferably a paper, a synthetic resin laminated paper, a polypropylenefilm or a polyester film. In this case, a thickness of the paperpreferably ranges between 20 μm and 200 μm inclusive. More preferably,the thickness thereof ranges between 40 μm and 170 μm inclusive, andfurther preferably, ranges between 60 μm and 150 μm inclusive. Athickness of the synthetic resin laminated paper preferably rangesbetween 30 μm and 220 μm inclusive. More preferably, the thicknessthereof ranges between 50 μm and 200 μm inclusive, and furtherpreferably, ranges between 70 μm and 180 μm inclusive. In this case, athickness of the polypropylene film preferably ranges between 15 μm and250 μm inclusive. More preferably, the thickness thereof ranges between30 μm and 230 μm inclusive, and further preferably, ranges between 50 μmand 200 μm inclusive. A thickness of the polyester film preferablyranges between 15 μm and 250 μm inclusive. More preferably, thethickness thereof ranges between 30 μm and 220 μm inclusive, and furtherpreferably, ranges between 50 μm and 190 μm inclusive.

The retroreflective sheet laminate of the present invention as anexample of a pattern of product to be shipped may be manufactured by,for example, peeling off the heat-resistant release material from alaminate of the retroreflective sheet of the present invention and theheat-resistant release material, which is manufactured by theabove-described method, followed by adhering a resin release film to thepressure-sensitive adhesive layer of the retroreflective sheet. In thiscase, for example, after forming the pressure-sensitive adhesive layer,the heat-resistant release material may be peeled off, and the resinrelease film may be adhered there, and then aging treatment may beperformed at 23±2° C. and a relative-humidity of 65±5% for 7 days.Alternatively, after forming the pressure-sensitive adhesive layer, theaging treatment may be performed for 7 days, and subsequently, theheat-resistant release material may be peeled off, and the resin releasefilm may be adhered there. The aging treatment for 7 days may beperformed separatively before and after the adhesion of the resinrelease film. In particular, the aging treatment is preferably performedat 23±2° C. and a relative humidity of 65±5% for 7 days, after theadhesion of the resin release film.

An example of a method for manufacturing the retroreflective sheet ofthe present invention will be specifically described with reference tothe drawings. FIGS. 1 to 7 show processes of an example of a method formanufacturing the retroreflective sheet of the present invention.

For a retroreflective element, a transparent bead having a reflectivemirror on a hemisphere part thereof, a cube corner type retroreflectiveelement and the like can be used. Here, a case of using the transparentbead having the reflective mirror at the hemisphere part will beillustrated. Hereinafter, a capsule lens type retroreflective sheet willbe illustrated, in which the transparent bead is supported so that thehemisphere part covered with the reflective mirror may be embedded inthe resin support sheet, although the retroreflective element is held inat least one of the resin support sheet and the cover film as mentionedabove. In the case of the cube corner type retroreflective element, itis held in the cover film.

Primarily, a reflective mirror is formed at a hemisphere part of thetransparent bead. As shown in FIG. 1, plural transparent glass beads 2as the transparent beads are embedded in a surface ofglass-beads-temporarily-fixing layer 7 made of polyethylene, which islaminated on a polyester film 8 as a first film. For embedding, alaminate of the glass-beads-temporarily-fixing layer 7 and the polyesterfilm 8 is heated so as to soften polyethylene, thereby sinking the glassbeads 2 into the glass-beads-temporarily-fixing layer 7. As mentionedabove, the glass bead 2 is one example of the transparent bead. Examplesof the transparent bead include a glass bead, a transparent resin beadand the like. Among them, a glass bead is preferable. A particlediameter of the transparent bead ranges, for example, from approximately5 μm to 300 μm, preferably ranges from approximately 20 μm to 90 μm, andmore preferably ranges from 40 μm to 80 μm. A refractive index of thetransparent bead ranges, for example, approximately 1.8 to 2.1,preferably ranges approximately 1.9 to 1.95, and more preferably rangesfrom 1.92 to 1.93.

Next, on hemisphere surfaces of the glass beads 2, which are exposedfrom the surface of the glass-beads-temporarily-fixing layer 7, a metalreflective layer 3 is formed by an vapor deposition method. Since thisvapor deposition is performed on the whole surface of theglass-beads-temporarily-fixing layer 7, the metal reflective layer 3 isformed not only on the surfaces of the glass beads 2, but also on thesurface of the glass-beads-temporarily-fixing layer 7. Examples of amaterial of the metal reflective layer 3 include aluminium, gold,silver, copper, nickel, chromium, tin, an alloy including these metals,titanium oxide, titanium nitride and the like, which have excellentreflectivities. Among them, aluminium is particularly preferable.

Examples of the retroreflective sheet of the present invention includetwo types of retroreflective sheets having the following configurations:

-   (A) including a primer layer 5 provided on a rear face of the resin    support sheet 4 (see FIG. 2); and-   (B) not including a primer layer 5 on a rear face of the resin    support sheet 4.

A pressure-sensitive adhesive layer is laminated on the rear face of theprimer layer 5 in the case of (A), or on the rear face of the resinsupport sheet 4 in the case of (B). In order to transfer the glass beads2 in the glass-beads-temporarily-fixing layer 7 to the resin supportsheet 4, a high molecular-weight or low molecular-weight plasticizer orthe like may be used for the resin support sheet 4. These plasticizersand the like are transferred to an interface between thepressure-sensitive adhesive layer and the resin support sheet 4, or tothe pressure-sensitive adhesive layer over the course of time, therebydegrading a sticking property of the pressure-sensitive adhesive layer.This leads to deterioration of an interfacial sticking property betweenthe pressure-sensitive adhesive layer and the resin support sheet 4,deterioration of a sticking property of the pressure-sensitive adhesivelayer to the substrate, and the like. The primer layer 5 may be used forsolving this problem, that is, for preventing the plasticizer and thelike from transferring from the resin support sheet 4 to thepressure-sensitive adhesive layer.

A resin for forming the resin support sheet 4 may be a thermoplasticresin or a thermosetting resin. The thermosetting resin is preferably acombination of a resin having a functional group, for example, aself-cross-linking type resin having one or plural functional groups ora resin having at least one functional group, and a hardening agenthaving a functional group that can react with these functional groups.In order to improve a spreading property and an adherence of the glassbeads, a silane coupling agent, for example, a resin with relatively lowmolecular weight having a polar group can be added to the thermosettingresin. In the resin for forming the resin support sheet 4, a totalweight of the resin having a functional group and the hardening agent ismore than 50% of weight parts of the resin for forming the resin supportsheet 4, and preferably more than 70% thereof.

Examples of the resin having a functional group include an acrylicresin, a fluororesin, a vinyl copolymer such as a styrene copolymer, apolycondensation copolymer such as a polyester resin and a polyurethaneresin. The functional group denotes a reactive functional group that canreact with a component of the hardening agent, or a self-cross-linkingfunctional group. Examples of the reactive functional group that reactswith the component of the hardening agent include a hydroxyl group, acarboxyl group, an epoxy group, an isocyanate group, an amino group, anacid amide group, an unsaturated double bond and the like. Examples ofthe self-cross-linking functional group include a hydrolyzable silylgroup, a N-methylolacrylamide group, an alkyletherifiedN-methylolacrylamide group, an unsaturated double bond and the like.

When the reactive functional group is a group having a so-called activehydrogen atom, such as a hydroxyl group, a carboxyl group, an aminogroup and an acid amide group, the hardening agent may be an isocyanatehardening agent, an aminoplast hardening agent, a polyepoxy compound, anacid anhydride or the like. When the reactive functional group is anepoxy group or the like, the hardening agent may be polyamine, polybasicacid or the like. When the reactive functional group is an isocyanategroup, the hardening agent may be various polyhydroxy compounds such asglycol and the like.

Moreover, when the reactive functional group is a so-calledself-cross-linking functional group such as a hydrolyzable silyl group,a cross-linking accelerator may be used additionally. This cross-linkingaccelerator is a catalyst for hydrolyzation or condensation of thishydrolyzable silyl group. Examples of this cross-linking acceleratorinclude: various acid compounds such as sulfuric acid, hydrochloric acidand phosphoric acid; an amine compounds such as monomethylamine andtriethylamine; various organic tin compounds such as di-n-butyl tindilaurate, di-n-butyl tin diacetate, di-n-butyl tin dioctoate, and thelike.

Examples of the resin for forming the primer layer 5 include a resinhaving a functional group that is for forming the resin support sheet,and a resin and a hardening agent selected from the above-notedhardening agents having functional groups that react with those resinsand the functional groups of those resins. The resin for the primerlayer 5 preferably has an excellent interlayer adhesiveness with respectto the resin support sheet 4.

The primer layer 5 can be obtained by, for example, applying a solutionof the resin for forming the primer layer on a polyester film 6 that isseparately prepared as a second film, and drying by, for example, ahot-air drier. The second film is an example of a support in apreferable manufacturing method of the present invention. A thickness ofthe primer layer 5 after being dried ranges, for example, from 3 μm to100 μm, and preferably ranges from 6 μm to 50 μm. The thickness of 3 μmor more is preferable because an effect of preventing the transfer ofthe plasticizer or the like can be enhanced. The thickness of 100 μm orless is also preferable because workability such as the adhesion of theretroreflective sheet can be improved.

Next, the resin support sheet 4 is formed on the face of the primerlayer 5 (FIG. 2). For a resin for forming the resin support sheet 4, anyof the resin having a functional group and the resin having nofunctional group can be used, but the resin having a functional group ispreferable.

The resin support sheet 4 can be obtained by, for example, applying thesolution of the resin for forming the resin support sheet on the primerlayer 5, and drying by, for example, a hot-air drier (see FIG. 2). Athickness of the resin support sheet 4 after being dried ranges, forexample, from 10 μm to 300 μm, and preferably ranges from approximately30 μm to 100 μm.

The retroreflective sheet of the type (B) having no primer layer 5 canbe obtained by omitting the process of forming the primer layer from themethod for manufacturing the retroreflective sheet.

Next, as shown in FIG. 3, a laminate of the polyester film 6, the primerlayer 5 and the resin support sheet 4 is disposed along a surface of theglass-beads-temporarily-fixing layer 7. Here, the resin support sheet 4disposed to be in contact with surfaces of the glass beads 2 of theglass-beads-temporarily-fixing layer 7, on which the metal reflectivelayer 3 is deposited.

Then, as shown in FIG. 4, the laminate is pressed onto the surface ofthe glass-beads-temporarily-fixing layer 7. This is performed so thatthe hemispheres of the glass beads 2 with the deposited metal reflectivelayer 3 may be embedded in the resin support sheet 4. Here, a couplingagent and the like further may be added to the resin support sheet 4 soas to improve adherence of the resin support sheet 4 to the glass beads2.

Then, as shown in FIG. 5, the glass-beads-temporarily-fixing layer 7 ispeeled off with the polyester film 8 from the surface of the resinsupport sheet 4. Here, as shown in FIG. 5, the glass beads 2 remain inthe resin support sheet 4, thereby being supported by the resin supportsheet 4 in a state where the hemispheres on which the metal reflectivelayer 3 is deposited are embedded. The metal reflective layer 3 that isprovided to the part other than the hemispheres of the glass beads 2exposed from the surface of the glass-beads-temporarily-fixing layer 7remains on the surface of the glass-beads-temporarily-fixing layer 7.

Subsequently, in the case where the primer layer 5 and/or the resinsupport sheet 4 include a hardening agent that is curable at a roomtemperature (for example, an isocyanate hardening agent or the like),aging treatment is preferably performed at a temperature between 30° C.and 40° C. so as to cure the primer layer 5 and/or the resin supportsheet 4. This step is for reducing variations in performance of aconnection part that is formed during the process of heat press embossforming, as well as for stabilizing a self-sustaining form thereafter.In addition, a heat treatment also may be performed at a temperaturebetween 120° C. and 150° C. in order to improve a fixation propertybetween the glass beads 2 and the resin support sheet 4.

Next, the surface of the resin support sheet 4 supporting the glassbeads 2, being in the state as illustrated in FIG. 6, is covered with atransparent cover film 1. For this cover film 1, a film with goodtransparency such as an unstretched acrylic film, a polyester resin, anacrylic resin, an alkyd resin, an urethane resin, a vinyl chlorideresin, a polycarbonate resin, a fluororesin, an acrylic silicon resinand the like can be used. Among them, the unstretched acrylic film isparticularly preferable.

For the cover film 1, films manufactured by a method other than acasting method, that is, any of well known methods such as an extrusionmethod and a calender method, also may be used. These films arestretched inevitably by at least 10% to 20% in a flowing direction ofthe films during the manufacture, according to its manufacturing method,but a film with minimal stretch is preferable.

It is preferable to use a thermoplastic resin as the cover film 1,because a heat sealing between the resin support sheet 4 and the coverfilm 1 can be performed well.

In the case where a resin that is not so suitable for heat sealing, forexample, some of thermosetting resins and fluororesins, a silicon resinor the like are used for the cover film 1, a laminate of a resin withhigh suitability for heat sealing and the above-mentioned resin may beused as the cover film 1.

When forming the cover film 1, an ultraviolet absorber and anantioxidant may be used in combination.

Heat press processing is performed from a polyester film 6 side of theresin support sheet 4 on which the cover film 1 disposed, using anpatterned embossing roll 9 (see FIG. 7). This heat pressing is suitablyperformed by passing through a heat roll. A surface temperature of theroll ranges, for example, from 150° C. to 240° C., and preferably rangesfrom 170° C. to 220° C. The surface temperature of 150° C. or higher ispreferable, because the heat pressing can be performed, the resinsupport sheet 4 and the cover film 1 can be adhered, and the resinsupport sheet 4 can maintain its self-sustaining form over a longperiod. The surface temperature of 240° C. or lower is preferable,because the polyester film 6 as the second film is not melted, and theworkability of the heat pressing can be improved.

After the process of heat press emboss forming, the polyester film 6 ispeeled off so as to obtain the original sheet of the retroreflectivesheet. Due to the process of heat pressing, an embossed groove 10 isformed on a rear face side of the resin support sheet 4. The groove has,for example, a width ranging from 200 μm to 800 μm and a depth rangingfrom 100 μm to 150 μm.

For the original sheet of the retroreflective sheet for composing theretroreflective sheet of the present invention, original sheets ofretroreflective sheets manufactured by various known methods may be usedas well as the original sheet of the capsule lens type retroreflectivesheet.

For example, as shown in FIG. 10, a capsule cube corner typeretroreflective sheet which is formed by heat may be used as theoriginal sheet of the retroreflective sheet. Also, a capsule cube cornertype retroreflective sheet including the cover film 1, a cube cornertype retroreflective elements 14 disposed on the rear face side of thecover film 1, a resin support sheet 4, and a connection part that isconnected by heat forming can be used.

Next, a pressure-sensitive adhesive layer is formed on a heat-resistantrelease material that is prepared separately. The pressure-sensitiveadhesive is as described above. For the release material, a known orconventional hard release paper can be used. Examples thereof include: abase material obtained by providing a filling layer on an original papersuch as a glassine paper, a clay coated paper, a kraft paper and awoodfree paper, with a thickness ranging from 30 μm to 100 μm; apolyethylene laminated paper with a thickness ranging from 50 μm to 200μm (manufactured by laminating a synthetic resin such as polyethyleneand polypropylene on a kraft paper, a woodfree paper or the like); and afilm of polypropylene, polyethylene terephthalate or the like with athickness ranging from 15 μm to 250 μm, on which a silicone resin, afluororesin or the like of emulsion type, solvent type or solventlesstype is applied, and a release agent layer is subsequently formed bycuring with heat, electron beams, ultraviolet or the like. Among theabove-noted release agents, the silicone resin is particularlypreferable. For a method for forming the release agent layer, aconventionally known method, for example, a comma coater, a bar coater,a gravure coater, a reverse roll coater or the like can be used asappropriate.

The pressure-sensitive adhesive layer 11 can be formed on theheat-resistant release material in the following manners. For example, asolution of the pressure-sensitive adhesive is applied on the face ofthe release agent layer of a release paper 12 as an example of therelease material, and is dried as necessary, thereby obtaining thepressure-sensitive adhesive layer 11.

For an apparatus for applying a pressure-sensitive adhesive, forexample, a reverse roll coater, a knife coater, a bar coater, a slot dyecoater, an air knife coater, a reverse gravure coater, a vario gravurecoater or the like can be used. An amount of the solution of thepressure-sensitive adhesive to be applied is adjusted so that athickness of the pressure-sensitive adhesive layer after being dried canbe in the range, for example, from 20 μm to 110 μm.

The solution of the pressure-sensitive adhesive may include thepressure-sensitive adhesive and the above-noted additives as necessary.For a solvent of the pressure-sensitive adhesive solution, commonly usedorganic solvents, for example, toluene, benzene, butyl acetate, ethylacetate, methylisobutylketone, methylethylketone, various kinds ofalcohol or the like can be used.

Next, the laminate of the release material and the pressure-sensitiveadhesive layer 11 is adhered to the original sheet of theretroreflective film. The method for the adhesion can be a commonlyknown method, for example, adhering by an adhesion roll that thepressure-sensitive adhesive layer 11 of this laminate faces the primerlayer 5 (or the resin support sheet 4 if omitting the primer layer 5) ofthe original sheet of the retroreflective sheet (see FIG. 8).

During this, when a roll temperature of an adhesion roll on the releasepaper side is set to be in a range, for example, from 50° C. to 90° C.,preferable range from 55° C. to 85° C., or more preferable range from60° C. to 80° C., the embossed groove 10 can be sufficiently filled witha part of the pressure-sensitive adhesive layer. The roll temperature of90° C. or lower is preferable because a damage such as shrinkageoccurring to the cover film 1 of the original sheet of theretroreflective sheet can be suppressed. Moreover, the roll temperatureof 50° C. or higher is also preferable because heat can be appliedeffectively. Here, an adhesion pressure ranges, for example, from 100N/cm to 800 N/cm, preferably ranges from 150 N/cm to 750 N/cm, morepreferably ranges from 200 N/cm to 700 N/cm. The adhesion pressure of100 N/cm or higher allows the grooves to be filled with thepressure-sensitive adhesive sufficiently, and the adhesion pressure of800 N/cm or lower can prevent a damage such as a press pressure appliedto the original sheet of the retroreflective sheet, thus beingpreferable.

Subsequently, the release paper 12 is peeled off. Heat-resistant releasematerials such as the release paper 12 generally have poor flexibility.In such a case, it is preferable to peel off the heat-resistant releasematerial and then adhere a resin release film 13 to thepressure-sensitive adhesive layer so as to obtain the retroreflectivesheet laminate of the present invention (see FIG. 9). Since the resinrelease film has excellent flexibility, even when the retroreflectivesheet laminate is wound longitudinally and then rewound, theretroreflective sheet laminate will hardly be curled. This is preferablebecause, when the retroreflective sheet laminate is subjected to aprocess such as printing, a phenomenon of partially swelling and peelinglike a tunnel between the retroreflective sheet and the resin releasefilm can be suppressed. The resin release film with excellentflexibility is as described above.

Alternatively, the pressure-sensitive adhesive layer 11 may be formeddirectly on the primer layer 5 of the original sheet of theretroreflective sheet, and the resin release film 13 may be disposed onthe pressure-sensitive adhesive layer 11. For example, the solution ofthe pressure-sensitive adhesive or a pressure-sensitive adhesive that isnot diluted with a solvent is applied on the primer layer 5 (or theresin support sheet 4 if omitting the primer layer 5) of the originalsheet of the retroreflective sheet, and is dried as necessary, therebyobtaining the pressure-sensitive adhesive layer 11. Since thepressure-sensitive adhesive used in this case has poor heat resistance,preferably it is curable by electron beams, ultraviolet or the like,without requiring heat dry. In this case, a coating layer of thesolution of the pressure-sensitive adhesive or the pressure-sensitiveadhesive that is not diluted with a solvent may be irradiated withelectron beams or ultraviolet so that the pressure-sensitive adhesivemay be cured, and the resin release film 13 may be subsequently adheredto the pressure-sensitive adhesive layer 11.

The present invention will be described below more specifically, withreference to examples and comparative examples, but the presentinvention is not limited to the below-described examples. In thefollowing description, “part” represents “part by weight”, and “%”represents “weight %”.

First, examples of preparing a resin that is necessary for manufacturingthe retroreflective sheet will be described.

Examples of preparing a resin having a functional group and a resinhaving no functional group

1. Preparation of a Solution (A-1) of an Acrylic Resin Having a HydroxylGroup

700 parts of toluene and 300 parts of n-buthanol were introduced into areactor provided with an agitator, a thermometer, a condenser and anozzle for introducing nitrogen gas, and was warmed up to 80° C. underan atmosphere of nitrogen. Then, a mixture containing 500 parts ofmethyl methacrylate, 400 parts of ethyl methacrylate, 100 parts of2-hydroxyethyl methacrylate, 8 parts of azobisisobutyronitrile and 5parts of tert-buthyl peroxy octoate (TBPO) was dropped over 4 hours.This was sustained at this temperature for 10 hours, then the solution(A-1) [nonvolatile content=50%; weight-average molecular weight=32,000;hydroxyl value=43 mg KOH/g solid; equivalent weight of reactivefunctional groups calculated from the hydroxyl value=1,300 (solid)] ofthe acrylic resin having the hydroxyl group was obtained.

2. Preparation of a Solution (A:-1) of an Acrylic Resin Having NoFunctional Group

A solution (A′-1) (nonvolatile content: 50%, and weight-averagemolecular weight: 81,000) of an acrylic resin having no functional groupwas obtained, in the same manner as the example of preparing thesolution (A-1) of the acrylic resin having the hydroxyl group, exceptusing “700 parts of methylmethacrylate and 300 parts of ethylacrylate”instead of “500 parts of methylmethacrylate, 400 parts ofethylmethacrylate and 100 parts of 2-hydroxyethylmethacrylate”, using 5parts of azobisisobutyronitrile instead of “8 parts” thereof, and using2 parts of tert-buthyl peroxy octoate (TBPO) instead of “5 parts”thereof.

3. Example of Preparing a Solution (A-2) of an Acrylic Resin Having aHydroxyl Group

1,000 parts of water, 200 parts of styrene, 200 parts ofn-butylacrylate, 100 parts of 2-hydroxyethylmetacrylate, 20 parts of 1%solution of polyvinyl alcohol (average polymerization degree: 100) and 2parts of azobisisobutyronitrile were introduced into the same apparatusas that in the example (A-1). The mixture thereof was agitated so as tokeep the system in suspension, and subsequently the system was warmed upto 80° C. and reacted at the temperature for 4 hours.

Next, a suspended solution obtained after the reaction was washed withwater, the water was drained, and then the suspended solution was dried,thereby obtaining a resin in a form of bead. 400 parts of this resin wasdissolved into 1,600 parts of toluene, thereby obtaining a solution(A-2) [nonvolatile content=20%; weight-average molecular weight=250,000;hydroxyl value=86 mg KOH/g solid; equivalent weight of reactivefunctional groups calculated from the hydroxyl value=652 (solid)] of anacrylic resin having a hydroxyl group.

4. Example of Preparing a Solution (A-3) of a Fluororesin Having aHydroxyl Group

1,000 parts of xylene, 10 parts ofbis(1,2,2,6,6-pentamethylpiperidinyl)sebacate, tert-butylperoxypivalate,200 parts of cyclohexylvinylether, 230 parts of ethylvinylether and 70parts of 4-hydroxybutylvinylether were introduced into a stainlessautoclave with interior capacity of 5,000 ml. Then nitrogen gas wasinjected into the autoclave so as to replace the air therein.

Furthermore, 500 parts of hexafluoropropylene extracted by liquidationwas introduced into the autoclave. After sealing the autoclave, atemperature therein was maintained at 60° C., and a reaction was carriedout for 15 hours, thereby obtaining a solution (A-3) [nonvolatilecontent=50%; weight-average molecular weight=42,500; hydroxyl value=67mg KOH/g solid; equivalent weight of reactive functional groupscalculated from the hydroxyl value=840 (solid)] of a fluororesin

5. Example of Preparing a Solution (A-4) of a Polyester Resin Having aHydroxyl Group

130 parts of ethylene glycol, 114 parts of neopentylglycol, 100 parts of1,6-hexanediol, 48 parts of trimethylolpropane, 720 parts of isophthalicacid and 0.5 parts of dibutyl tin oxide were introduced into a reactorthat is provided with an agitator, a thermometer, a rectifier and anozzle for introducing nitrogen gas. A temperature of a system in thereactor was increased to 220° C., maintained for 3 hours, and furtherincreased to 240° C., and thereafter, a dehydration reaction wasperformed while the temperature was maintained for 6 hours.Subsequently, the temperature of the system was decreased to 130° C.,and then 1,000 parts of hexylene was added into the reactor, therebyobtaining a polyester resin solution (A-4) [nonvolatile content=50%;weight-average molecular weight=47,000; hydroxyl value=10 mg KOH/gsolid; equivalent weight of reactive functional groups calculated fromthe hydroxyl value=5,650 (solid)].

Following measuring methods are adopted in the examples of the presentinvention.

(1) Yamamoto's Cohesion Test

A Yamamoto's cohesion tester shown in FIG. 12 was used. This apparatushas a width of 520 mm, a height of 345 mm and a depth of 140 mm, inwhich a retroreflective sheet 26 was disposed with a pressure-sensitiveadhesive layer facing down and being adhered to an adherend 21, andloads 22 and 23 were respectively connected to both ends of theretroreflective sheet 26 via strings that were hang over a load pulley24 and a side pulley 25, respectively. A jig 32 with a core 30 of anelectric micrometer 31 attached thereto was provided on the adherend 21and the retroreflective sheet 26. Reference number 27 represents aclamping screw, 28 represents a micrometer, 29 represents a coil, 34represents a display, and 35 represents a core holding block. FIG. 13 isa schematic perspective view showing a connection between theretroreflective sheet 26 and the strings in the tester shown in FIG. 12.Reference number 36 represents an pressing roller, and 37 represents astring.

Using the Yamamoto's cohesion tester, a specimen obtained by cutting theretroreflective sheet 26 with a width of 10 mm (a size of 10 mm×5 mm)was adhered to a mirror-surfaced flat plate of a SUS304 steel platespecified by JISG4305 with a width of 5 mm. Here, the adhesion wascarried out by reciprocating the automatic roller 36 three times at apressing speed of 5 mm/sec, which was specified by 10.2.4 in JISZ0237and 2 kg in weight. Immediately after the pressing, loads of 17 g (theloads 22 and 23) were imposed to the both ends of the specimen via thestrings. Subsequently, a measurement load of 200 g was further imposedto the load 22, and after 5 minutes, displacement (initial displacement)was measured. After 5 minutes from the imposition of the measurementload, the load of 200 g was removed. Displacement remaining after 10minutes from the removal (residual displacement) was measured so as toobtain a residual rate. Here, the residual rate (%) was defined as (theresidual displacement/the initial displacement)×100. The measurementcondition was at 23±2° C. and at 65±5% in relative humidity.

(2) Share Holding Power Test

A holding power test was performed in accordance with the holding powertest of JISZ0237. More specifically, the test was performed as followsusing a SUS304 stainless steel plate as an adherend. Under atmosphere of23±2° C. in temperature and 65±5% in relative humidity, a rubber rollerof 2 kg in weight was reciprocated three times so as to press theretroreflective sheet onto the stainless steel plate. An area to beadhered was 25 mm×25 mm. After being left for 25 minutes, the stainlesssteel with the retroreflective sheet adhered thereto was kept being hungvertically for 1 hour in a holding power testing machine that was set tobe at 40° C. After the elapse of 1 hour, a load of 9.8 N was imposed to(hung from) the retroreflective sheet, which was 1.568 N/cm².Thereafter, time interval (fall time) from a time of imposing the loadto a time of fall of the retroreflective sheet from the stainless steelplate was measured. When the fall time is 24 hours or longer, thedisplacement was measured at the time when 24 hours passed.

EXAMPLE 1

In a surface of a 25 μm-thick glass-beads-temporarily-fixing layer madeof polyethylene which was laminated on a polyester film (a first film),plural glass beads (retroreflective elements, particle diameter: 45-80μm, and refractive index: 1.92-1.93) were embedded, so that the glassbeads may be embedded into the surface of theglass-beads-temporarily-fixing layer by approximately 25% to 35% of aparticle diameter thereof. The glass-beads-temporarily-fixing layer andthe polyester film were softened by heat so as to embed the glass beads.Thereafter, aluminum was evaporated onto a surface of hemisphere partsof the glass beads exposed from the surface of theglass-beads-temporarily-fixing layer, thereby forming a reflectivemirror.

Next, a solution containing: 83 parts by weight of an acrylic copolymersolution (solid: 50%) with a solvent of toluene and butyl acetate; and17 parts by weight of methyletherified methylol melamine (solid: 60%)was applied onto a polyethylene terephthalate (polyester) film(thickness: 50 μm) as a second film that was prepared separately, andsubsequently was dried using a hot-air drier, thereby forming a primerlayer with a thickness of approximately 20 μm. The acrylic copolymer wasconsist of methyl methacrylate (PA), ethyl acrylate (EA), butyl acrylate(BA) and 2-hydroxyethylmethacrylate (2-HEMA). Thereafter, a blendedsolution that mainly contains the solution (A-1) of the acrylic resinhaving the hydroxyl group was applied on this primer layer, and wasdried using a hot-air drier, thereby forming a resin support sheet witha thickness of approximately 60 μm.

Content of the blended solution will be described as follows.

-   (1) 100 parts of the solution (A-1) of the acrylic resin having a    hydroxyl group (solid: 50%)-   (2) 11 parts of methyletherified methylol melamine (solid: 60%)-   (3) 25 parts of rutile type titanium dioxide-   (4) 13 parts of an acrylic resin for dispersing a pigment (solid:    50%)-   (5) 1 part of a silane coupling agent.

Subsequently, a laminate of the polyester film (the second film), theprimer layer and the resin support sheet was disposed on a metaldeposition face side of the glass-beads-temporarily-fixing layer, sothat the resin support sheet may be in contact with the surface of theglass beads in the glass-beads-temporarily-fixing layer. Thereafter, thelaminate was pressed onto the surface of theglass-beads-temporarily-fixing layer. This pressing was performed sothat the reflective mirror of the glass beads may be embedded into theresin support sheet. For the pressing, the laminate on which the resinsupport sheet was disposed was rolled by a heat roll with a surfacetemperature of 170° C.

Next, the glass-beads-temporarily-fixing layer was peeled off with thepolyester film (the first film) from the surface of the resin supportfilm, thereby obtaining a laminate. Subsequently, the thus obtainedlaminate was subjected to a heat treatment at 140° C. in order toimprove an adhesiveness between the glass beads and the resin supportsheet. The resin support sheet in which the hemispheres of the glassbeads were embedded was covered with an uniaxially stretched (with astretching ratio of 1.3, but substantially unstretched) transparentacrylic film (a cover film, manufactured by Kaneka Corporation) on theglass beads side, thereby obtaining a laminate. Thereafter, the thusobtained laminate was embossed by heat, being rolled from the polyesterfilm (the second film) side, using an patterned embossing roll, with aroll surface temperature of 210° C. After this hot press emboss forming,the polyester film (the second film) was peeled off, so that an originalsheet of a retroreflective sheet was obtained.

A solution of a pressure-sensitive adhesive was prepared by blending andstirring: 100 parts by weight of an acrylic resin (trade name:AROSET8964, manufactured by Nippon Shokubai Co., Ltd.), which containeda solid of 47 wt % and a high softening point tackifier and had an amidegroup, as a resin for a pressure-sensitive adhesive; and 0.2 parts byweight of a modified polyisocyanate resin (trade name: CORONATE L-55E,manufactured by Nippon Polyurethane Industry Co., Ltd.) as a hardeningagent. The solution of the pressure-sensitive adhesive was applied ontoa hard release paper (trade name: EKR-780, manufactured by LintecCorporation), and was dried by heat at 70° C. for 1 minute and at 100°C. for 2 minutes, thereby forming a pressure-sensitive adhesive layerwith a thickness of approximately 80 μm. Thereafter, a face of theprimer layer of the original sheet of the retroreflective sheet and aface of the pressure-sensitive adhesive layer of the laminate composedof the release paper and the pressure-sensitive adhesive layer wereadhered to each other, being rolled at an adhesion pressure of 450 N/cmand at a roll surface temperature of 70° C. A groove formed on theprimer layer by the hot press emboss forming was filled with a part ofthe pressure-sensitive adhesive layer. Subsequently, the release paperwas peeled off, and a flexible polypropylene (PP) release film (tradename: FILMBINA PP-S-80, manufactured by Fujimori Kogyo Co., Ltd.,thickness: 80 μm, Young's modulus: 800 MPa) was adhered there, thusobtaining a retroreflective sheet laminate. The obtained retroreflectivesheet laminate was subjected to aging under a condition of 23±2° C. and65±5% of relative humidity for 7 days.

EXAMPLE 2

An original sheet of a retroreflective sheet was manufactured in thesame manner as Example 1, except that the content of the blendedsolution for the resin support sheet was as follows, and the heattreatment to be performed after embedding the glass beads into the resinsupport sheet was omitted.

-   (1) 100 parts of the solution (A-2) of the acrylic resin having a    hydroxyl group (solid: 20%)-   (2) 6.0 parts of methyletherified methylol melamine (solid: 60%)-   (3) 10 parts of rutile type titanium dioxide-   (4) 5 parts of an acrylic resin for dispersing a pigment (solid:    50%)-   (5) 2 parts of polyester plasticizer

Next, a pressure-sensitive adhesive layer was formed in the same manneras Example 1, except using 100 parts by weight of an acrylic estercopolymer resin with a solid of 58 wt % (trade name: SK DYNE 1576,manufactured by Soken Chemicals & Engineering Co., Ltd.) and 5.1 partsby weight of an epoxy hardening agent (trade name: E-05C, manufacturedby Soken Chemicals & Engineering Co., Ltd.) as a resin for thepressure-sensitive adhesive, so that a retroreflective sheet laminatewas obtained. Thereafter, aging treatment was performed under the samecondition as Example 1.

EXAMPLE 3

An original sheet of a retroreflective sheet was obtained in the samemanner as Example 1, except that the formation of the primer layer wasomitted, the content of the blended solution for the resin support sheetwas changed as follows, the thickness of the resin support sheet waschanged from 60 μm to 80 μm, and aging treatment was additionallyperformed at 30° C. for 1 month, after the glass beads were embeddedinto the resin support sheet and subjected to the heat treatment at 140°C.

-   (1) 100 parts of a polyester resin (A-4) (solid: 50%)-   (2) 2.5 parts of HMDI-based isocyanurate (solid: 75%, NCO: 15%)-   (3) 25 parts of rutile type titanium dioxide-   (4) 12 parts of an acrylic resin for dispersing a pigment (solid:    50%)

Next, a pressure-sensitive adhesive layer was formed in the same manneras Example 1, except using 0.25 parts of CORONATE L-55E (trade name)manufactured by Nippon Polyurethane Industry Co., Ltd. as a hardeningagent, so that a retroreflective sheet laminate was obtained.Thereafter, aging treatment was performed under the same condition asExample 1.

EXAMPLE 4

(Example of Using an Uncured Resin Sheet as the Resin Support Sheet)

An original sheet of a retroreflective sheet was obtained in the samemanner as Example 1, except that the formation of the primer layer wasomitted, the content of the blended solution for the resin support sheetwas as follows, the thickness of the resin support sheet was changedfrom 60 μm to 80 μm.

-   (1) 100 parts of the solution (A:-1) of the acrylic resin (solid:    50%)-   (2) 25 parts of rutile type titanium dioxide-   (3) 13 parts of an acrylic resin for dispersing a pigment (solid:    50%)-   (4) 5 parts of polyester plasticizer

Next, a pressure-sensitive adhesive layer was formed in the same manneras Example 2, except using 5.5 parts of E-05C (trade name) manufacturedby Soken Chemicals & Engineering Co., Ltd., as a hardening agent, sothat a retroreflective sheet laminate was obtained. Thereafter, agingtreatment was performed under the same condition as Example 1.

COMPARATIVE EXAMPLE 1

An original sheet of a retroreflective sheet was obtained in the samemanner as Example 1, and then a pressure-sensitive adhesive layer wasmanufactured in a method described below. A solution of apressure-sensitive adhesive was prepared by blending and stirring: 100parts by weight of an acrylic alkyl ester copolymer resin (trade name:AROSET HI-81D, manufactured by Nippon Shokubai Co., Ltd), whichcontained 39 wt % of a solid and had an interpenetrating polymer networkstructure, as a resin for a pressure-sensitive adhesive; and 1.2 partsby weight of a hardening agent (trade name: CORONATE L-55E, manufacturedby Nippon Polyurethane Industry Co., Ltd.). The solution of thepressure-sensitive adhesive was applied onto a hard release paper, andwas dried, thereby forming a pressure-sensitive adhesive layer with athickness of approximately 80 μm. Thereafter, a face of the primer layerof the original sheet of the retroreflective sheet and a face of thepressure-sensitive adhesive layer of the laminate composed of therelease paper and the pressure-sensitive adhesive layer were adhered toeach other, being rolled at an adhesion pressure of 450 N/cm and at aroll surface temperature of 70° C. A groove formed on the primer layerby the hot press emboss forming was filled with a part of thepressure-sensitive adhesive layer. Subsequently, the release paper waspeeled off, and a flexible polypropylene (PP) release film (trade name:FILMBINA PP-S-80, manufactured by Fujimori Kogyo Co., Ltd., thickness:80 μm, Young's modulus: 800 MPa) was adhered there, thus obtaining aretroreflective sheet laminate. Thereafter, aging treatment wasperformed under the same condition as Example 1.

COMPARATIVE EXAMPLE 2

An original sheet of a retroreflective sheet was obtained in the samemanner as Example 1. Subsequently, a solution of a pressure-sensitiveadhesive was prepared by blending and stirring: 100 parts by weight ofan acrylic resin (trade name: AROSET HI-91D-3, manufactured by NipponShokubai Co., Ltd.), which contained a solid of 40 wt % and had acarboxylic acid as a functional group and chlorinated PP and PE thatwere grafted, as a resin for a pressure-sensitive adhesive; and 0.3parts by weight of a hardening agent (trade name: CORONATE L-55E,manufactured by Nippon Polyurethane Industry Co., Ltd.). Theretroreflective sheet laminate was obtained in the same manner ascomparative Example 1 except that the solution of the pressure-sensitiveadhesive was applied onto a hard release paper, and was dried by heat soas to form a pressure-sensitive adhesive layer with a thickness ofapproximately 40 μm. Thereafter, aging treatment was performed under thesame condition as Example 1.

COMPARATIVE EXAMPLE 3

An original sheet of a retroreflective sheet is obtained in the samemanner as Example 1. Subsequently, a retroreflective sheet laminate wasobtained in the same manner as Comparative example 2, except using 100parts by weight of an acryl-vinyl acetate copolymer resin (trade name:SAIVINOR AT-208, manufactured by Saiden Chemical Industry Co., Ltd.)with a solid of 43 wt % as a resin for a pressure-sensitive adhesive,and 1 part of a solution containing 2.2% ofN,N,N′,N′-tetraglycidyl-m-xylenediamine (toluene: 91.9%, IPA: 5.9%)(trade name: A-9, manufactured by Saiden Chemical Industry Co., Ltd.) asa hardening agent. Thereafter, aging treatment was performed under thesame condition as Example 1.

Physical properties of the obtained retroreflective sheet laminate willbe shown in Table 1 and 2. A “thickness of the pressure-sensitiveadhesive layer” in Table 1 means “a thickness of the pressure-sensitiveadhesive layer at a part where a groove is not formed on a rear face ofthe resin support sheet”. TABLE 1 Thickness of the pressure-sensitiveFilling state of the adhesive layer Residual rate pressure-sensitive(μm) Holding power (%) adhesive layer Example 1 80 2.0 mm/70 hrs 26.7 CExample 2 80 2.2 mm/55 hrs 29.4 C Example 3 80 1.9 mm/115 hrs 34.6 CExample 4 80 2.3 mm/98 hrs 36.2 C Comparative 80 0.1 mm/>168 hrs 9.2 Dexample 1 Comparative 40    —/2 hrs 65.8 D example 2 Comparative 40 0.4mm/>168 hrs 27.5 E example 3

TABLE 2 Appearance Method-1 Method-2 Method-3 Immediately After leavingin Immediately After leaving in Immediately After leaving in after theatmosphere at 60° C. after the atmosphere at 60° C. after the atmosphereat 60° C. manufacture for 24 hours manufacture for 24 hours manufacturefor 24 hours Example 1 C C C C C C Example 2 C C C C C C Example 3 C C CC C C Example 4 C C C C C C Comparative C D C D C D example 1Comparative C D C D C D example 2 Comparative C D C D C D example 3(Remarks)

(1) Holding power: (length of displacement after 24 hours)/(fall time)

(2) Filling state of the pressure-sensitive adhesive layer: the flexiblepolypropylene (PP) release film of the retroreflective sheet laminatewas peeled off, and then a state of filling the pressure-sensitiveadhesive layer into the grooves that were formed on the primer layer orthe resin support sheet by the hot press emboss forming was visuallyobserved.

Standard of Evaluation

C: The filling rate of the pressure-sensitive adhesive layer was in arange from 70 to 100%.

D: The filling rate of the pressure-sensitive adhesive layer was 50% ormore, and lower than 70%.

E: The filling rate of the pressure-sensitive adhesive layer was lowerthan 50%.

(3) Standard of Appearance Evaluation

C: Abnormality such as wrinkles, blisters, bubbles and exfoliations wasnot observed on the surface of the retroreflective sheet.

E: Abnormality such as wrinkles, blisters, bubbles and exfoliations wasobserved on the surface of the retroreflective sheet.

(Method for an Appearance Test)

Method 1

The retroreflective sheet was adhered to an aluminium plate (thickness:1 mm) with size of 650 mm×1000 mm, using a KIWALITE Hand Squeeze RollApplicator HSA2-130 which has a nip roll with a hardness of 60 (measuredby a JIS K 6301 A type hardness meter) and a rubber with a thickness of10 mm, a diameter of 110 mm and a rubber face length of 1270 mm, so asto manufacture a specimen. Appearance of a surface of the specimen wasobserved both immediately after the adhesion and after being left inatmosphere at 60° C. for 24 hours.

An adhesion pressure during the use of the above-mentioned Hand SqueezeRoll Applicator HSA2-130 was 0.4 MPa, which was measured by using aKIWALITE Pressure Scaling Film.

Method-2

The retroreflective sheet was adhered to an aluminium plate (thickness:1 mm) with a size of 650 mm×1000 mm, using a KIWALITE Hand Squeeze RollApplicator HSA2-130 which has a nip roll with a hardness of 25 (measuredby a JIS K 6301 A type hardness meter) and a rubber with a thickness of10 mm, a diameter of 110 mm and a rubber face length of 1270 mm, so asto manufacture a specimen. Appearance of a surface of the specimen wasobserved both immediately after the adhesion and after being left inatmosphere at 60° C. for 24 hours.

An adhesion pressure during the use of the above-mentioned Hand SqueezeRoll Applicator HSA2-130 was 0.1 MPa or lower, which was measured by aKIWALITE Pressure Scaling Film.

Method-3

As shown in FIG. 11, three aluminum plates (thickness: 1 mm) with a sizeof 68 mm×148 mm and an aluminum plate (thickness: 1 mm) with a size of330 mm×330 mm were disposed on an aluminum plate (thickness: 1 mm) witha size of 600 mm×800 mm, and preparing a substrate that has acharacteristic of distorting the retroreflective sheet compulsively whenthe sheet was adhered. Thereafter, the retroreflective sheet with a sizeof 340 mm×660 mm was adhered so that an edge thereof may be at aposition of 100 mm away from an part A on the substrate, using aKIWALITE Hand Squeeze Roll Applicator HSA2-130 which has a nip roll witha hardness of 60 (measured by a JIS K 6301 A type hardness meter) and arubber with a thickness of 10 mm, a diameter of 110 mm and a rubber facelength of 1270 mm. Subsequently, the retroreflective sheet was cut alongthe aluminium plate (thickness: 1 mm) with the size of 330 mm×330 mm soas to manufacture a specimen. Appearance of a surface of the specimenwas observed both immediately after the adhesion and after being left inatmosphere at 60° C. for 24 hours.

An adhesion pressure during the use of the above-mentioned Hand SqueezeRoll Applicator HSA2-130 was 0.4 MPa or lower, which was measured byusing a KIWALITE Pressure Scaling Film.

From the above-stated results of Examples and Comparative examples, itwas found that, when the groove on the rear face of the resin supportsheet, which was formed by the hot press emboss forming, was filled witha part of the pressure-sensitive adhesive layer, and when the residualrate and the fall time of the pressure-sensitive adhesive layer were inthe predetermined ranges, abnormality such as wrinkles, blisters,bubbles and exfoliations was not observed on the surface of theretroreflective sheet, and problems of the conventional products can besolved.

INDUSTRIAL APPLICABILITY

The retroreflective sheet of the present invention is prevented from anappearance abnormality such as wrinkles and blisters, which occurs overtime after being adhered to a substrate, thus being useful for trafficsigns, guide signs, sign boards for safety guidance, or other safetysigns.

1. A retroreflective sheet, comprising: plural retroreflective elements;a resin support sheet; a transparent cover film disposed on a surfaceside of the resin support sheet; and a pressure-sensitive adhesive layerformed on a rear face side of the resin support sheet, wherein theretroreflective elements are held in at least one of the resin supportsheet and the cover film, the resin support sheet and the cover film areconnected to each other by heat press emboss forming from the rear faceside of the resin support sheet so as to form a connection part, agroove of the connection part is formed on the rear face side of theresin support sheet, the groove is filled with a part of thepressure-sensitive adhesive layer, a residual rate of thepressure-sensitive adhesive layer ranges between 10% and 50% inclusive,and a fall time of the pressure-sensitive adhesive layer ranges between10 hours and 150 hours inclusive, where the residual rate (%)=(aresidual displacement÷an initial displacement)×100, the initialdisplacement represents a displacement (mm) between a flat plate and theretroreflective sheet measured by a Yamamoto's cohesion tester, whichoccurs after 5 minutes from steps of: pressing the retroreflective sheetwith a size of 10 mm×5 mm onto the mirror-surfaced flat plate of aSUS304 steel plate specified by JISG 4305 with a width of 5 mm, using apressing device specified by JIS Z 0237; adding loads of 17 grespectively to both ends of the retroreflective sheet via stringsimmediately after the pressing; and further applying a measurement loadof 200 g to one of the loads, the residual displacement represents adisplacement occurring between the flat plate and the retroreflectivesheet after 10 minutes from removal of the load of 200 g, and the falltime represents a fall time of the retroreflective sheet with a load of9.8 N imposed in a holding power test at 40° C. in accordance with aJISZ0237 holding power test.
 2. The retroreflective sheet according toclaim 1, wherein a filling factor of the pressure-sensitive adhesivelayer in the groove is 50% or more, where the filling factor(%)=[(A−B)÷A]×100, wherein the letter A denotes an area of the grooveper unit area of the retroreflective sheet, and the letter B denotes anarea of an opening gap formed on an interface between the groove and thepressure-sensitive adhesive layer per unit area of the retroreflectivesheet.
 3. The retroreflective sheet according to claim 1, wherein theresidual rate ranges between 15% and 45% inclusive.
 4. Theretroreflective sheet according to claim 1, wherein the fall time rangesbetween 20 hours and 140 hours inclusive.
 5. The retroreflective sheetaccording to claim 1, wherein a thickness of the pressure-sensitiveadhesive layer at a part where the groove is not formed on the rear faceside of the resin support sheet ranges between 20 μm and 110 μminclusive.
 6. The retroreflective sheet according to claim 1, whereinthe pressure-sensitive adhesive layer is formed of a rubber-based resinor an acrylic resin.
 7. The retroreflective sheet according to claim 1,wherein the retroreflective element is a transparent bead of which ahemisphere part is covered with a reflective mirror, and is supported sothat the hemisphere part of the transparent bead covered with thereflective mirror may be embedded in the resin support sheet.
 8. Aretroreflective sheet laminate, comprising the retroreflective sheetaccording to claim 1 and a resin release film, wherein the resin releasefilm is laminated on the pressure-sensitive adhesive layer.
 9. Theretroreflective sheet laminate according to claim 8, wherein the resinrelease film is a flexible resin film with Young's modulus rangingbetween 50 MPa and 2000 MPa inclusive.
 10. The retroreflective sheetlaminate according to claim 9, wherein the flexible resin film is anunstretched polypropylene film or a low-density polyethylene film.
 11. Amethod for manufacturing a laminate of a heat-resistant release materialand the retroreflective sheet according to claim 1, comprising steps of:preparing an original sheet of a retroreflective sheet comprising pluralretroreflective elements, a resin support sheet, and a transparent coverfilm disposed on a surface side of the resin support sheet, wherein theretroreflective elements are held in at least one of the resin supportsheet and the cover film, the resin support sheet and the cover film areconnected to each other by heat press emboss forming from a rear face ofthe resin support sheet so as to form a connection part, and a groove ofthe connection part is formed on the rear face side of the resin supportsheet; forming a pressure-sensitive adhesive layer on the heat-resistantrelease material; and filling the groove of the resin support sheet witha part of the pressure-sensitive adhesive layer, by disposing theheat-resistant release material with the pressure-sensitive adhesivelayer formed thereon on the rear face side of the original sheet of theretroreflective sheet and adhering by inter-roll line pressure rangingbetween 100 N/cm and 800 N/cm inclusive at a roll surface temperatureranging between 50° C. and 90° C. inclusive from a heat-resistantrelease material side.
 12. The manufacturing method according to claim11, comprising a further step of performing aging treatment to thepressure-sensitive adhesive layer at 23±2° C. and a relative humidity of65±5% for 7 days.
 13. The manufacturing method according to claim 11,wherein the heat-resistant release material is one selected from thegroup consisting of: a paper with a thickness ranging between 20 μm and200 μm inclusive, a synthetic resin laminated paper with a thicknessranging between 30 μm and 220 μm inclusive, a polypropylene film thathas a thickness ranging between 15 μm and 250 μm inclusive, and apolyester film that has a thickness ranging between 15 μm and 250 μminclusive.
 14. A method for manufacturing a laminate comprising theretroreflective sheet according to claim 1 and a resin release film,comprising the steps of: preparing an original sheet of retroreflectivesheet comprising plural retroreflective elements, a resin support sheet,and a transparent cover film disposed on a surface side of the resinsupport sheet, wherein the retroreflective elements are held in at leastone of the resin support sheet and the cover film, the resin supportsheet and the cover film are connected to each other by heat pressemboss forming from a rear face of the resin support sheet so as to forma connection part, and a groove of the connection part is formed on therear face side of the resin support sheet; forming a pressure-sensitiveadhesive layer on a side of a heat-resistant release material; fillingthe groove of the resin support sheet with a part of thepressure-sensitive adhesive layer, by disposing the heat-resistantrelease material with the pressure-sensitive adhesive layer formedthereon on the rear face side of the original sheet of theretroreflective sheet and adhering by inter-roll line pressure rangingbetween 100 N/cm and 800 N/cm inclusive at a roll surface temperatureranging between 50° C. and 90° C. inclusive from a heat-resistantrelease material side; peeling off the heat-resistant release materialand; adhering a resin release film in place of the heat-resistantrelease material.
 15. The method according to claim 14 for manufacturingthe retroreflective sheet laminate, comprising a further step ofperforming aging treatment to the pressure-sensitive adhesive layer at23±2° C. and a relative humidity of 65±5% for 7 days.